under-identification test for instrumental var

[StarryCatte]

I'm now using feols() to estimate a regression with instrumental variable.
The number of instrumental variable is less than the number of endogenous variable.
How can I test whether the equation is under identified, for example, using Kleibergen-Paap rk LM statistics?

[kylebutts]

Are you misspeaking here? A regression with fewer instrumental variables than endogenous variables should not be able to produce a coefficient estimate. The testing procedure is for the over-identified case where the number of instruments is larger than the number of endogenous variables